It is known that coordination complexes of transition metals are very good catalysts for a wide variety of reactions including, particularly, hydrogenation, hydroformylation and olefin oxidation. When these reactions are carried out in the liquid phase, the coordination complexes used as catalysts are almost invariably in a dissolved state in the reaction medium. Inasmuch as the price of the metals used in these coordination complexes is high, it is necessary, from an economic standpoint, to recover such complexes from the reaction medium, since otherwise the cost of the reaction is economically unfeasible. A difficulty exists, however, in the fact that these necessary recovery operations are expensive in themselves. Many recovery operations have been suggested. Thus, the residues of the distillation of the reaction mixture, which contain the catalyst, can be recycled directly to the reaction, but this method is not very satisfactory; in fact, such a simple recycling results in substantial losses and significant poisoning of the catalyst complexes, taking into account the limited stability of such complexes. Other techniques of recovering such complexes have also been suggested, such as separation by osmosis, insolubilization, etc.
Because of the difficulty of the separation procedures as noted above, it has also been suggested that recovery could be avoided if the coordination complexes were adsorbed on solid supports so as to reduce their concentration in the reaction mixture. Classical supports have been suggested for this purpose, but commercialization has not yet been achieved, presumably because of the poor experimental results which have heretofore been obtained by using the classical supports.
In the work leading up to the present invention, applicants studied such classical supports and determined that they are generally unsatisfactory in that they either serve to inhibit the development of the desired reactions to be catalyzed and/or they do not satisfactorily serve to retain the coordination complex catalysts out of solution. Thus, it has been determined that while alumina and silica involve practically no reduction in the yield of the catalyzed reaction, they have a very weak power of retention of the complexes, so that the complexes are found predominantly in the reaction effluent. On the other hand, it has been determined that various activated carbons retain the catalyst in a suitable manner, but serve to practically entirely inhibit the desired reactions.